The present invention relates to lift truck mast assemblies. More particularly, the present invention relates to a mast assembly which provides maximum operator visibility while concurrently providing substantial free-lift of the carriage without extension of the mast uprights.
Most commercial lift trucks have mast supported carriages which are lifted by means of hydraulic jacks, chain drives, or combinations of both systems. One problem often presented by such lift trucks is that of limited operator visibility. The usually required centralized placement of the carriage lift systems relative to the supporting mast often blocks the vision of an operator located in the cab or operator station of the lift truck.
Another problem presented by such lift trucks is that of excessive unextended mast height. Lift trucks are often required to negotiate tight turns in limited ceiling areas. This requires that such vehicles present a relatively low profile and low center of gravity when moving from one load space to another. However, by providing a relatively low fixed mast assembly to increase low ceiling maneuverability, the maximum lift height for loading may be prohibitively restricted.
Some attempts have been made in the prior art to address both of these problems. Examples of such prior art attempts are found in U.S. Pat. Nos. 3,394,778; 3,127,956; 2,58l,791; and 2,456,320, to Brinton, Hosbein, et al; Gilman; and Repke, respectively. None of these patents, however, disclose inventions which simultaneously solve the noted problems while at the same time providing a relatively inexpensively fabricatable, extremely efficient and functional mast assembly.
The present invention simultaneously improves operator visibility while providing a mast assembly having a low profile during maneuvering with high extension capability when desired.